if you look at the map of Roshar (the one just before the prelude), it's in the southern hemisphere, and there are latitude lines indicating that the equator is just north of the Reshi Island. Also, Shinovar is at 30-40 degrees south, so theoretically it should have the same seasonal variation as the area between Florida and Northern California.
Come to think of it, we still don't know if the relative day/night lengths change with the seasons (which would indicate a seriously erratic axial tilt).